Where to start

[LindenLongRods]

I have totally rebuilt a 1971 18hp Evinrude. (powerhead, Carb, waterpump, lower unit. Just can't get it started. I don't know where to set the carburetor screws. It turns over but doesn't stay running. Very smoky too, someone told me to put a little extra oil in gas for the first run. Any suggestions?

 

[F_R]

3/4 turns open on the high speed and 1-1/2 on the slow speed will get it running. Adjust from there, once running. "Extra" oil from what? 50:1 is normal spec. 24:1 won't hurt, but necessity is a matter of opinion.

 

[racerone]

Is there a high speed mixture screw on a 71 model 18 HP ??----Test for strong spark.---Try switching plug leads.

 

[LindenLongRods]

Is there a high speed mixture screw on a 71 model 18 HP ??----Test for strong spark.---Try switching plug leads.

Yes there is only one screw mixture screw i think
, just not sure where to set. Should I turn all the way in and back off a certain amount? I changed caps, points and condensers. The plug leads are definitely right.

 

[racerone]

Does spark jump a gap of 5/16" on a TEST DEVICE . ?----Is the high speed jet found screwed into the very bottom of the float bowl clean, yes or no ?

 

[oldboat1]

Ha! thought I lost this pic. With both plugs out, you might look for 3/4" spark, then close the gap until you see a strong sharp spark. 5/8" is what you need:
Don't get the closed style (inline).

 

[racerone]

Doubt that the points / condenser magneto on a 71 model 18 HP can jump a gap of 5/8".----Look for 5/16" as a very good spark on these !!

 

[oldboat1]

agree. intended to restate #5 info.

 

[lindy46]

Did you change fuel pump? Tank vented?

 

[LindenLongRods]

Did you change fuel pump? Tank vented?

I rebuilt the fuel pump, it is getting gas. yes tank is vented.

 

[LindenLongRods]

I will try again this weekend. I want to check points and condensors. Make sure no wires are pinched.

 

[LindenLongRods]

I'm getting good bright blue spark. That rules out points, condensors right?

 

[Crosbyman]

ok you got fire and fuel.....

what about compression #s
now you need to get the gas inside the cylinders....

do you feel a good suction on the carb face ? my understanding of carbs is that the first shot of "fumes" comes from choking and the top idle passage idle chamber/drip holes ....have they been check ?

is the choke fully closing? and is it releasing...

will it stay running if you pump the fuel bulb ? yes===> bad fuel pump !!!

see picture for potential carb issues (older carb picture but same basic issues )

 

[racerone]

When choke plate is closed a very low pressure develops in the carburetor when you pull the rope.----Then the atmospheric pressure in the float bowl floods the carburetor throat with fuel.

 

[Crosbyman]

agree... yet in start mode after the choke plate opens up the fuel mostly comes from the idle cct part of the carb until given throttle .

it should idle after starting

 

[LindenLongRods]

I got it running I bypassed the fuel pump. I ordered a new one. but low idle it coughs very hard. My carburetor only has 1 screw for oil/gas mixture. Also what is running tempeture? I don't feel it is getting enough water throughout head. Water was boiling when I splashed the head. I rebulit water pump

 

[oldboat1]

You are overheating (over 160F). Get an infrared tester -- look for 120-130F.
water pump rebuild is suspect. Key in place? Tube in grommet at pump?
Run in a barrel (water about half way up the leg) or on the boat -- muffs won't do it for you.)
Carb adjustment at the top would be for air/fuel mix. Set it at about one turn open to start (1 to 1 1/2).
Wait for the replacement fuel pump for more testing. Use a 50:1 gas to oil ratio. Mix a gallon at a time for testing.
Measure the spark, as indicated (tests strength of magneto).

 

[LindenLongRods]

I rebuilt water pump. still had problem took off lower unit and did drill test. It worked when I sunk lower unit almost all the way to pump housing. I don't remember having to do that before. I'm going to look at head make sure no build up. Maybe reverse fins on impellor? or in the gear housing? I rebuilt that too, could something be wrong down there?

 

[hardwater fisherman]

Water has to be at least 6 inches above the pump as they are not self priming. It is hard to tell but I think the motor is not deep enough in your barrel.

 

[LindenLongRods]

Water has to be at least 6 inches above the pump as they are not self priming. It is hard to tell but I think the motor is not deep enough in your barrel.

I will take head off to make sure not blocked up and lower unit make sure pipe in in grommet. I will take better pics and also video. Thank you so much so far guys